web: add basic ASP.NET Core web interface

PluralKit.Web/Pages/Index.cshtml.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace PluralKit.Web.Pages
+{
+    public class IndexModel : PageModel
+    {
+        public void OnGet()
+        {
+        }
+    }
+}